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I've seen a lot of "low budget" green screen setups. However, when I watch things about professional filmmaking, it seems everyone is using blue screens instead. (e.g. I've seen Industrial Light and Magic called "the blue screen boys", and the recent TF2 "Sentry Sabotage" video was filmed using a blue screen)

Is there some technical reason for this distinction or is it merely personal preference/inertia?

4 Answers
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Professional film productions use neither only green nor only blue for chroma keying, but switch between both depending on the scene. Each can only be used when there are no objects of the same colour in view, otherwise it takes extra work to un-remove these objects. Blue and green are the usual colours because the human skin, which is what will almost always need to remain visible, is very different from both, but this is not the only thing shown in chroma key scenes!

In most situations, you have neither blue nor green objects in the foreground so both colours will, in principle, work. But they may not work equally well. The main reason why green is predominant in digital productions: digital cameras can resolve green light best, so it's possible to do proper green chroma-keying even with a cheap camera that might have problems to resolve a blue screen accurately enough. But that's not a concern in professional film productions. Analog cameras actually resolve blue better, but the difference is not really significant.
Especially blond hair will sometimes reflect much of the light coming from a greenscreen behind, which can lead to weird and somewhat ill-looking green shades. Blue is less problematic in that aspect. On the other hand, clothing will more often feature blueish colours than greenish ones.

"Green chroma screens have become more and more popular in recent years, largely because green provides a brighter color channel that tends to have less noise than the blue channel. The relative brightness of green makes it a bad choice for shooting blonde hair though, which is a lot easier to key against blue backgrounds."

"The bluescreen has some distinct advantages. When you can’t avoid a lot of spill (for example when you have to put the foreground very close to the chroma material) you can take advantage of the fact that we tend to find blue casts less disturbing than people walking around looking sea-sick with green faces. Also, when shooting for something that will be composited on to outdoor backgrounds and water, a slight blueish cast won’t be a problem."

The Lord of the Rings used green screen. That's the last behind the scenes I've seen, however I can't imagine it being 'most' if that's the case. Looking at the wiki article there are a couple that use blue but if you think about it I imagine it all comes down to what the actor is wearing and if there are any sets pieces involved.

Green may be best for some situations and blue others.

As for weather forcasters specifically, which color do you see being a problem because of their attire; neon green or blue? =)